Field of the Invention
The present invention relates, to a surface processing apparatus and a dry etching method using a neutral beam, and particularly to a surface processing apparatus capable of effecting surface processing such as etching on an object to be processed without any damage with high accuracy and to a dry etching method.
There is known a dry etching apparatus capable of bringing a neutral beam into an etchant as one of surface processing apparatuses.
As the dry etching apparatus, there is known one shown in FIG. 30, which has been disclosed in Japanese Patent Application Laid-Open Publication No. 62-259443, for example, wherein a positive ion beam corresponding to the rare gas is extracted into a vacuum chamber 154 by an ion extracting electrode 152 from a plasma generated in an ion source 150 using a d.c. discharge or a high-frequency discharge, the rare-gas ion beam is converted into a rare-gas neutral beam (also hereinafter called a "neutral particle beam") by a resonance charge-exchange reaction between the rare-gas ion and neutral rare gas comprised of elements similar to the rare-gas ions in the vacuum chamber 154, and a substrate S to be processed is irradiated with the neutral beam thereby to etch the substrate S.
A pair of deflecting electrodes 158 is provided in the dry etching apparatus referred to above. Ions produced by the charge-exchange reaction and ions which have been extracted from a plasma source and remain unchanged, are deflected by the deflecting electrodes 158 so that they do not reach the substrate S. Incidentally, reference numeral 156 in the drawing indicates a turbo-molecular pump.
As other dry etching apparatus, there is known one shown in FIG. 31, which has been disclosed in Japanese Patent Application Laid-Open Publication No. 1-120826, for example, wherein negative ions produced by an electron attachment reaction from a plasma generated within a discharge tube 164 using a microwave input from a microwave oscillator 160 through a waveguide 162, are extracted into a vacuum chamber 166 in beam form, a beam of the negative ions is converted into a neutral beam by a charge-exchange reaction, and a substrate S to be processed is irradiated with the neutral beam through grid electrodes 168 thereby to etch the substrate S. Incidentally, reference numeral 170 in the drawing indicates a vacuum pump.
In the disclosed dry etching apparatus, deflecting magnets and the ion retarding electrodes (grid electrodes) 168 are respectively provided in front of the substrate S to be processed in order to prevent electrons and ions from reaching the substrate S.
A demand for uniformly processing the surface of an object to be processed originally exists in each of the surface processing apparatuses which start with the dry etching apparatuses disclosed in the above publications.
However, even in the case of all dry etching apparatuses disclosed in the above-described publications, the ion beam extracted from the plasma is diverged by the coulomb repulsion exerting between respective charged particles in the ion beam while the ion beam is being transported within the vacuum chamber. Therefore, the neutral particle beam produced by converting the ion beam into the neutral beam is also diverged. As a result, uniform processing and high anisotropic processing cannot be effected on the substrate even if the neutral particle beam is caused to reach the substrate according to the degree of divergence of the neutral particle beam. Thus, a fine pattern cannot be etched with high accuracy.
In particular, the ion beam is made more divergent so long as increases in transporting distance and beam flux are made or a reduction in beam energy is made.
Even when, on the other hand, the neutral particle beam is produced by either one of the charge-exchange reaction and the electron attachment reaction, the efficiency of reaction is made high as the relative speed or velocity between respective mutually-reacted particles decreases. Further, the energy (also hereinafter called merely "energy") of translational motion of the ion beam may be set as low as possible to reduce etching damage caused by a collision between an etchant and the substrate.
According to the above construction, the production of the neutral particle beam having the low energy and the high flux and the attainment of the uniform high anisotropic processing are contrary to each other depending on the conventional dry etching apparatuses. Therefore, a problem arises that both the production and the attainment cannot be met simultaneously.
Since the ion beam is always made divergent as described above during transportation, the diverged neutral beam is merely obtained in principle. However, particularly when the ion beam is removed by the deflecting electrodes 158 alone as in the case of the dry etching apparatus shown in FIG. 30, the neutral particles produced by the charge-exchange reaction inherit or take over the direction of the ion beam as it is upon charge exchange. Therefore, when ions each having the moving direction unorthogonal to an object S to be processed are converted into neutral particles while the ion beam is being transported, the converted neutral particles reach unorthogonally to the object S. It is thus impossible to etch a high-precision and fine pattern. Further, surface processing is ununiformly effected along the direction of the surface of the object S, so that the unevenness on processing tends to occur in its surface. It is therefore necessary to equally bring the neutral beam which reaches the object S into alignment using a certain means in order to carry out high-precision and fine etching processing.
In the surface processing apparatus shown in FIG. 31, a plurality of mesh-like ion retarding electrodes (also called "mesh electrodes") 168 are provided in front of the object (substrate) S to be processed. Therefore, the direction of the neutral beam transmitted through the ion retarding electrodes 168 can be restricted to some degree by bringing the positions of fine holes defined in the respective mesh electrodes into substantial alignment and using the ion retarding electrodes 168 as a collimator. Thus, higher-precision and fine etching can be effected on the object S to be processed.
Further, the present applicant has filed U.S. application Ser. No. 07/896,371, now abandoned wherein a micro channel plate is used as the collimator.
When, however, the collimator (ion retarding electrodes) 168 comprised of the plurality of mesh electrodes and the like is used, the neutral beam can pass through the fine holes of the collimator but is cut off or blocked by areas of portions about the holes. Therefore, the surface of the object S corresponding to the portions about the holes is brought into a shadow at which the neutral beam hardly reaches.
Thus, when the etching is effected with the ion retarding electrodes 168 and the like as the collimator in the above surface processing apparatus, higher-precision and fine processing can be carried out. However, each pattern corresponding to each fine hole of the collimator is transferred onto the object S and hence the unevenness is produced upon etching processing, thus the uniform processing cannot be carried out. The unevenness on processing cannot be removed even if the transmission rate of the collimator is raised beyond need. When the direction of the neutral beam is made even, the unevenness is produced even in the case of one ion retarding electrode.
In the surface processing apparatuses shown in FIGS. 30 and 31 for irradiating the object S with the neutral beam using the ion deflecting electrodes 158 or the ion retarding electrodes 168, when the object S to be processed is replaced by another to effect the next process, it is necessary to stop the irradiation of the object S with the neutral beam for each processing and replace the object S with another. To stop the irradiation of the object S with the neutral beam, it is only necessary to stop the ion beam. As ion-beam stopping methods, there are known one (1) for stopping the generation of a plasma serving as an ion beam source, one (2) for stopping the supply of a voltage to the ion extracting electrode 152, and one (3) for disposing a shutter used for shielding the ion beam during the transportation of the ion beam.
In the method (1), however, the matching between a power source for generating the plasma and the produced plasma is made for each processing. Therefore, a long period of time is required until the plasma is made stable. Therefore a throughput for processing is reduced. Further, the condition of generation of the plasma for each processing varies and there is a potential problem that stable processing conditions cannot be obtained.
In the method (2), the following problem arises. When the ion beam is being extracted from the plasma by the ion extracting electrode 152, a portion of the ion beam collides with the ion extracting electrode 152 thereby to raise the temperature thereof and allow a variation in shape such as a warp to occur in the ion extracting electrode 152. Since, however, the ion extracting electrode 152 takes a stable form at a certain position, an ion beam having quality corresponding to the form of the ion extracting electrode 152 is produced. Thus, when the application of the voltage to the ion extracting electrode 152 is stopped for each processing, the stable ion beam cannot be obtained, thus causing a problem that the uniform processing cannot be effected for each object S to be processed.
In the method (3), it is unnecessary to stop the generation of the plasma and the extracting of the ion beam for each processing. Therefore, this method is excellent in terms of the stability of quality of the ion beam as compared with the above two methods. However, sputtering occurs due to the irradiation of the shutter with the ion beam, so that the dry etching apparatus is filled with materials of the shutter as fine particles. Therefore, a clean process for the object S to be processed is prevented by such fine particles. Further, in the surface processing apparatus shown in FIG. 31, since the ion beam does not reach the ion retarding electrodes 168, a thermal variation in shape occurs in each of the ion retarding electrodes 168 similarly to the ion extracting electrode. Therefore, conditions for allowing the neutral beam to pass through the ion retarding electrodes 168 vary for each processing.
Thus, each of the methods of (1) through (3) is accompanied by a problem that the uniform processing cannot be effected on the object to be processed for each processing.